AbstractA long term multifrequency campaign on the T Tauri star RU Lupi has been carried out in the X-Ray, UV optical and IR spectral regions with ASTRON and IUE satellites and ESO 1.5 m+IDS, 1.4 m CAT, 0.5 m UBVRI and 1 m IR telescopes, respectively.We present two flare-like events occurred on April 17, 1984 and June 30, 1986. The first one was detected only in the UV, clue to lack the of simultaneous observations in other spectral regions. The second one was observed in UV, optical and IR regions showing a maximum roughly in the U band A comparison of the whole energy distribution of this event with that of a quiescent state observed on June 27 shows a flux enhancement of (89 ± 2)%. A detailed analysis of UV continuum and lines, namely N V, C I, CII, CIV, Si II and Si IV, shows that ihe surfaces fluxes of RU Lupi are always larger than those observed on typical flare stars and on the Sun by a factor of roughly 2 and 3 orders of magnitude, respectively. This fact allows us to conclude that RU Lupi activity cannot be explained even invoking a complete coverage by solar-like plages. On the contrary a patchy distribution of the emitting regions could explain the observed behaviour of this active star.
Photometric variability of the T Tauri star TW Hya on time-scales of hours to years★